Aliphatic polyester resin composition, preparation method therefor, and molded article and foamed article produced from the resin composition

ABSTRACT

An aliphatic polyester resin composition is provided which is excellent in heat resistance, moldability and hydrolysis resistance. The aliphatic polyester resin composition comprises a biodegradable polyester resin (A) essentially including an α- and/or β-hydroxycarboxylic acid unit and crosslinked by at least one crosslinking agent (B) selected from the group consisting of (meth)acrylate compounds and polyvalent isocyanate compounds, wherein some or all of carboxyl groups of the resin (A) are blocked by 0.01 to 20 parts by mass of a terminal blocking agent (C) based on 100 parts by mass of the resin (A).

TECHNICAL FIELD

The present invention relates to an aliphatic polyester resincomposition, a preparation method therefor, and a molded article and afoamed article produced from the resin composition. Particularly, theinvention relates to an aliphatic polyester resin composition whichcomprises a crosslinked biodegradable polyester resin with its terminalcarboxyl groups at least partly blocked and is excellent in heatresistance, moldability and hydrolysis resistance, and to a preparationmethod for the resin composition and a molded article and a foamedarticle produced from the resin composition.

BACKGROUND ART

Polylactic acids are more excellent in heat resistance with higher glasstransition temperatures (Tg) than other biodegradable resins, but theheat resistance of the polylactic acids in a temperature range higherthan Tg is not necessarily high. Since the polylactic acids have lowercrystallization rates, the molding cycle for injection molding should beincreased. Further, the polylactic acids have lower melt viscosities, sothat molding conditions are significantly limited. Therefore, themolding productivity is relatively low.

For improvement of the heat resistance and the productivity, theinventors of the present invention previously proposed inJP-A-2003-128901 and JP-A-2003-238789 that a biodegradable polyester iscrosslinked by addition of a (meth)acrylate compound or a polyvalentisocyanate compound. Further, the inventors proposed in JP-A-2003-147182that a layered silicate is additionally used.

On the other hand, JP-A-2001-261797 discloses a technique for improvingthe heat resistance and the hydrolysis resistance by blocking terminalcarboxyl groups of a polylactic acid by a specific carbodiimidecompound.

The heat resistance and moldability of the polylactic acids are improvedby the crosslinking and the addition of the layered silicate. However,the polylactic acids fail to maintain their physical properties due tohydrolysis during prolonged storage or during use under severely humidand hot conditions. Therefore, the practicality of the polylactic acidsis not sufficient under such conditions.

Further, the polylactic acid with its terminal groups blocked by thecarbodiimide compound as disclosed in JP-A-2001-261797 is not suitablefor production of injection molded articles, foamed articles andblow-molded articles.

DISCLOSURE OF THE INVENTION

To solve the aforesaid problems, it is an object of the presentinvention to provide an aliphatic polyester resin composition excellentin heat resistance, moldability and hydrolysis resistance, a preparationmethod therefor, and a molded article produced from the resincomposition.

The inventors of the present invention have found that the aforesaidproblems are solved only by utilizing the crosslinking and the terminalgroup blocking of a biodegradable aliphatic polyester resin incombination, and attained the present invention.

The present invention is summarized as follows:

(1) An aliphatic polyester resin composition comprising a biodegradablepolyester resin (A) which essentially comprises an α- and/orβ-hydroxycarboxylic acid unit and crosslinked by at least onecrosslinking agent (B) selected from the group consisting of(meth)acrylate compounds and polyvalent isocyanate compounds, whereinsome or all of carboxyl groups of the resin (A) are blocked by 0.01 to20 parts by mass of a terminal blocking agent (C) based on 100 parts bymass of the resin (A).

(2) In the aliphatic polyester resin composition (1), the terminalblocking agent (C) comprises at least one compound selected from thegroup consisting of carbodiimide compounds, epoxy compounds, oxazolinecompounds, oxazine compounds and aziridine compounds.

(3) In the aliphatic polyester resin composition (1), the crosslinkingagent (B) is present in a proportion of 0.01 to 10 parts by mass basedon 100 parts by mass of the biodegradable polyester resin (A).

(4) In the aliphatic polyester resin composition (1), the biodegradablepolyester resin (A) essentially comprises one of poly(L-lactic acid),poly(D-lactic acid), a copolymer of L-lactic acid and D-lactic acid anda blend of poly(L-lactic acid) and poly(D-lactic acid).

(5) The aliphatic polyester resin composition (1) further comprises 0.05to 30 parts by mass of a layered silicate based on 100 parts by mass ofthe biodegradable polyester resin (A).

(6) A method for preparing the aliphatic polyester resin composition (1)comprises: mixing a biodegradable polyester resin (A) and a terminalblocking agent (C) and then mixing a crosslinking agent (B) with theresulting mixture.

(7) A molded article or a foamed article is produced from any of thealiphatic polyester resin compositions (1) to (5)

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph illustrating a relationship between crystallinity (θ)and time (minute) for determining a crystallization rate index accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will hereinafter be described in detail.

The biodegradable polyester resin (A) to be used in the presentinvention essentially comprises an α- and/or β-hydroxycarboxylic acidunit. Examples of the α- and/or β-hydroxycarboxylic acid unit includeL-lactic acid, D-lactic acid, glycolic acid, 3-hydroxybutyric acid,3-hydroxyvaleric acid and 3-hydroxycaproic acid, among which L-lacticacid, D-lactic acid or a mixture of L-lactic acid and D-lactic acid ispreferred for industrial mass production.

Therefore, the biodegradable polyester resin (A) to be used in thepresent invention is poly(L- and/or D-lactic acid), poly(glycolic acid),poly(3-hydroxybutyric acid), poly(3-hydroxyvaleric acid) orpoly(3-hydroxycaproic acid), or a copolymer or a blend of any of thesepolymers.

In consideration of the mechanical strength and heat resistance of anarticle molded from the inventive aliphatic polyester resin composition,the α- and/or β-hydroxycarboxylic acid unit is preferably present in aproportion of not smaller than 50 mol %, more preferably not smallerthan 60 mol %, most preferably not smaller than 75 mol %, in thebiodegradable polyester resin (A). The biodegradable polyester resin (A)preferably has a melting point of not lower than 120° C., morepreferably not lower than 150° C. The melting point can be controlled byproperly selecting the type and amount of the hydroxycarboxylic acidunit.

The biodegradable polyester resin (A) is prepared by a known meltpolymerization method, as required, in combination with a solid statepolymerization method. Poly(3-hydroxybutyric acid) andpoly(3-hydroxyvaleric acid) may be microbiologically prepared.

As required, another biodegradable resin component may be copolymerizedor blended with the poly(α- and/or β-hydroxycarboxylic acid) as themajor component of the biodegradable polyester resin (A), as long as theheat resistance of the poly(α- and/or β-hydroxycarboxylic acid) is notdeteriorated. Examples of the biodegradable resin component includealiphatic polyesters such as polyethylene succinate and polybutylenesuccinate which are prepared from a diol and a dicarboxylic acid,poly(ω-hydroxyalkanoates) such as poly(ε-caprolactone), poly(butylenesuccinate-co-butylene terephthalate) and poly(butyleneadipate-co-butylene terephthalate) which are biodegradable even witharomatic components, polyester amides, polyester carbonates, andpolysaccharides such as starch. A non-biodegradable resin component maybe copolymerized or blended with the poly(α- and/or β-hydroxycarboxylicacid) without departing from the scope of the present invention.

The molecular weight of the biodegradable polyester resin is notparticularly limited, but the biodegradable polyester resin preferablyhas a weight average molecular weight of not smaller than 50,000 and notgreater than 1,000,000, more preferably not smaller than 80,000 and notgreater than 1,000,000. If the weight average molecular weight issmaller than 50,000, the melt viscosity of the resin composition is toolow. On the other hand, if the weight average molecular weight isgreater than 1,000,000, the moldability of the resin composition isreduced.

The crosslinking agent (B) to be used for crosslinking the biodegradablepolyester resin (A) comprises at least one crosslinking agent selectedfrom the group consisting of (meth)acrylate compounds and polyvalentisocyanate compounds. The (meth)acrylate compounds and the polyvalentisocyanate compounds may be used in combination.

Preferred examples of the (meth)acrylate compounds include a compoundwhich contains two or more (meth)acryl groups in its molecule and acompound which contains one or more (meth)acryl groups and one or moreglycidyl groups or vinyl groups in its molecule. These compounds arehighly reactive with the biodegradable polyester resin (A), and providea resin composition less liable to contain residual monomers and lessliable to be colored. Specific examples of the (meth)acrylate compoundsinclude glycidyl methacrylate, glycidyl acrylate, glyceroldimethacrylate, trimethylolpropane trimethacrylate, trimethylolpropanetriacrylate, allyloxypolyethylene glycol monoacrylate,allyloxypolyethylene glycol monomethacrylate, ethylene glycoldimethacrylate, diethylene glycol dimethacrylate, polyethylene glycoldimethacrylate, polyethylene glycol diacrylate, polypropylene glycoldimethacrylate, polypropylene glycol diacrylate and polytetramethyleneglycol dimethacrylate (whose alkylene glycol moiety may containcopolymerized alkylenes having various molecular lengths), butandiolmethacrylate and butandiol acrylate, among which ethylene glycoldimethacrylate, diethylene glycol dimethacrylate, polyethylene glycoldimethacrylate and polypropylene glycol dimethacrylate are preferred forthe safety and the reactivity.

Preferred examples of the polyvalent isocyanate compounds includecompounds which are highly reactive with the biodegradable polyesterresin (A) and provide a resin composition less liable to containresidual monomers. Specific examples of the polyvalent isocyanatecompounds include hexamethylene diisocyanate, tolylene diisocyanate,diphenylmethane diisocyanate, xylylene diisocyanate, naphthylenediisocyanate, isophorone diisocyanate, polyesters modified withpolyvalent isocyanates, poly(meth)acrylic acid compounds modified withpolyvalent isocyanates and compounds obtained by modifying polyvalentalcohols with polyvalent isocyanates, and mixtures of any of thesecompounds, among which hexamethylene diisocyanate and tolylenediisocyanate are preferred for the safety and the reactivity.

The aforesaid crosslinking agent (B) is preferably blended in thebiodegradable polyester resin (A) in a total amount of 0.01 to 10 partsby mass, more preferably 0.01 to 5 parts by mass, further morepreferably 0.01 to 1 part by mass, based on 100 parts by mass of thebiodegradable polyester resin (A). If the amount of the crosslinkingagent is smaller than 0.01 part by mass, the heat resistance and themoldability intended by the present invention cannot be provided. If theamount of the crosslinking agent is greater than 10 parts by mass, thecrosslinking degree is too high, so that the operability is reduced.

Where the polyvalent isocyanate compound is used as the crosslinkingagent (B), a blend amount of greater than 5 parts by mass may result indeterioration of the operability and the safety because an unreactedportion of the isocyanate compound is liable to evaporate. Further,reheating reduces the molecular weight of the resulting resincomposition. Therefore, the blend amount is preferably not greater than5 parts by mass based on 100 parts by mass of the biodegradablepolyester resin (A).

A method for the crosslinking by the crosslinking agent (B) is notparticularly limited, but the simplest method is such that thebiodegradable polyester resin (A) is melt-mixed with the crosslinkingagent (B). Where the biodegradable polyester resin (A) is melt-mixedwith the crosslinking agent (B), a peroxide is preferably added as acrosslinking assist agent for increasing the crosslinking degree.Preferred examples of the peroxide include organic peroxides which areexcellent in dispersibility in the resin. Specific examples of theorganic peroxides include benzoyl peroxide,bis(butylperoxy)trimethylcyclohexane,bis(butylperoxy)methylcyclododecane, butyl bis(butylperoxy)valerate,dicumyl peroxide, butyl peroxybenzoate, dibutyl peroxide,bis(butylperoxy)diisopropylbenzene, dimethyldi(butylperoxy)hexane,dimethyldi(butylperoxy)hexyne and butylperoxycumene. The peroxide ispreferably blended in the biodegradable polyester resin (A) in an amountof 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass,based on 100 parts by mass of the biodegradable polyester resin (A). Ifthe blend amount is smaller than 0.1 part by mass, the effect ofincreasing the crosslinking degree is reduced. A blend amount of greaterthan 10 parts by mass is not preferred in terms of costs.

In the inventive aliphatic polyester resin, some or all of carboxylgroups of the biodegradable polyester resin (A) should be blocked by theterminal blocking agent (C). A terminal blocking degree is notparticularly limited, but may be properly adjusted depending on theapplication of the resin. However, the ratio of the blocked terminalcarboxyl groups of the resin (A) is preferably not lower than 20%, morepreferably not lower than 50%, most preferably not lower than 90%, withrespect to the terminal carboxyl groups of the resin (A) before theterminal blocking.

A method for blocking the terminal carboxyl groups of the biodegradablepolyester resin (A) is to add a proper amount of a terminal blockingagent of a condensation type such as an aliphatic alcohol or an amidecompound into a polymerization system in the polymerization of the resinand cause a dehydration-condensation reaction at a reduced pressure. Foreasy control of the polymerization degree of the resin, however, it ispreferred to add a terminal blocking agent of an addition type uponcompletion of the polymerization or when the polymerized resin is meltedagain.

The terminal blocking agent of the addition type preferably comprises atleast one compound selected from the group consisting of carbodiimidecompounds, epoxy compounds, oxazoline compounds, oxazine compounds andaziridine compounds.

Specific examples of the carbodiimide compounds includeN,N′-di-2,6-diisopropylphenylcarbodiimide, N,N′-di-o-tolylcarbodiimide,N,N′-diphenylcarbodiimide, N,N′-dioctyldecylcarbodiimide,N,N′-di-2,6-dimethylphenylcarbodiimide,N-tolyl-N′-cyclohexylcarbodiimide,N,N′-di-2,6-di-tert-butylphenylcarbodiimide,N-tolyl-N′-phenylcarbodiimide, N,N′-di-p-nitrophenylcarbodiimide,N,N′-di-p-aminophenylcarbodiimide, N,N′-di-p-hydroxyphenylcarbodiimide,N,N′-di-cyclohexylcarbodiimide, N,N′-di-p-tolylcarbodiimide,p-phenylenebis-di-o-tolylcarbodiimide,p-phenylenebis-dicyclohexylcarbodiimide,hexamethylenebis-dicyclohexylcarbodiimide,4,4′-dicyclohexylmethanecarbodiimide, ethylenebis-diphenylcarbodiimide,N,N′-benzylcarbodiimide, N-octadecyl-N′-phenylcarbodiimide,N-benzyl-N′-phenylcarbodiimide, N-octadecyl-N′-tolylcarbodiimide,N-cyclohexyl-N′-tolylcarbodiimide, N-phenyl-N′-tolylcarbodiimide,N-benzyl-N′-tolylcarbodiimide, N,N′-di-o-ethylphenylcarbodiimide,N,N′-di-p-ethylphenylcarbodiimide,N,N′-di-o-isopropylphenylcarbodiimide,N,N′-di-p-isopropylphenylcarbodiimide,N,N′-di-o-isobutylphenylcarbodiimide,N,N′-di-p-isobutylphenylcarbodiimide,N,N′-di-2,6-diethylphenylcarbodiimide,N,N′-di-2-ethyl-6-isopropylphenylcarbodiimide,N,N′-di-2-isobutyl-6-isopropylphenylcarbodiimide,N,N′-di-2,4,6-trimethylphenylcarbodiimide,N,N′-di-2,4,6-triisopropylphenylcarbodiimide,N,N′-di-2,4,6-triisobutylphenylcarbodiimide, diisopropylcarbodiimide,dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide,t-butylisopropylcarbodiimide, di-β-naphthylcarbodiimide,di-t-butylcarbodiimide and aromatic polycarbodiimides. Other examples ofthe carbodiimide compounds include polymers of any of these compounds.These carbodiimide compounds may be used either alone or in combination.In the present invention, any of the aromatic carbodiimides, inparticular N,N′-di-2,6-diisopropylphenylcarbodiimide, or a polymer ofany of these compounds (having a polymerization degree of about 2 toabout 20) is desirably used. It is particularly preferred to use any ofthe carbodiimide compounds having a saturated cyclic structure such as acyclohexane ring, particularly 4,4′-dicyclohexylmethane carbodiimide, ora polymer of any of these compounds (having a polymerization degree ofabout 2 to about 20).

Examples of the epoxy compounds include

N-glycidylphthalimide, N-glycidyl-4-methylphthalimide,N-glycidyl-4,5-dimethylphthalimide, N-glycidyl-3-methylphthalimide,N-glycidyl-3,6,-dimethylphthalimide, N-glycidyl-4-ethoxyphthalimide,N-glycidyl-4-chlorophthalimide, N-glycidyl-4,5-dichlorophthalimide,N-glycidyl-3,4,5,6-tetrabromophthalimide,N-glycidyl-4-n-butyl-5-bromophthalimide, N-glycidylsuccinimide,N-glycidylhexahydrophthalimide,N-glycidyl-1,2,3,6-tetrahydrophthalimide, N-glycidylmaleinimide,N-glycidyl-α,β-dimethylsuccinimide, N-glycidyl-α-ethylsuccinimide,N-glycidyl-α-propylsuccinimide, N-glycidylbenzamide,N-glycidyl-p-methylbenzamide, N-glycidylnaphthamide,N-glycidylstearamide, N-methyl-4,5-epoxycyclohexane-1,2-dicarboxylimide,N-ethyl-4,5-epoxycyclohexane-1,2-dicarboxylimide,N-phenyl-4,5-epoxycyclohexane-1,2-dicarboxylimide,N-naphthyl-4,5-epoxycyclohexane-1,2-dicarboxylimide,N-tolyl-3-methyl-4,5-epoxycyclohexane-1,2-dicarboxyl imide,o-phenylphenyl glycidyl ether, 2-methyloctyl glycidyl ether, phenylglycidyl ether, 3-(2-xenyloxy)-1,2-epoxypropane, allyl glycidyl ether,butyl glycidyl ether, lauryl glycidyl ether, benzyl glycidyl ether,cyclohexyl glycidyl ether, α-cresyl glycidyl ether, p-t-butylphenylglycidyl ether, glycidyl methacrylate, ethylene oxide, propylene oxide,styrene oxide, octylene oxide, 2-ethylhexyl glycidyl ether, hydroquinonediglycidyl ether, resorcin diglycidyl ether, 1,6-hexandiol diglycidylether and hydrogenated bisphenol-A diglycidyl ether. Other examples ofthe epoxy compounds include diglycidyl terephthalate, diglycidyltetrahydrophthalate, diglycidyl hexahydrophthalate, dimethyl diglycidylphthalate, phenylene diglycidyl ether, ethylene diglycidyl ether,trimethylene diglycidyl ether, tetramethylene diglycidyl ether,hexamethylene diglycidyl ether, sorbitol diglycidyl ether, polyglycerolpolyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerolpolyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropanepolyglycidyl ether, resorcinol diglycidyl ether, neopentylglycoldiglycidyl ether, ethylene glycol diglycidyl ether, diethylene glycoldiglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycoldiglycidyl ether, dipropylene glycol diglycidyl ether, polypropyleneglycol diglycidyl ether and polybutadiene glycol diglycidyl ether.

One or two or more compounds may be arbitrarily selected from theseepoxy compounds for blocking the terminal carboxyl groups of thealiphatic polyester resin. In terms of the reactivity, ethylene oxide,propylene oxide, phenyl glycidyl ether, o-phenylphenyl glycidyl ether,p-t-butylphenyl glycidyl ether, N-glycidylphthalimide, hydroquinonediglycidyl ether, resorcin diglycidyl ether, 1,6-hexandiol diglycidylether, hydrogenated bisphenol-A diglycidyl ether, ethylene glycoldiglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexandioldiglycidyl ether and trimethylolpropane polyglycidyl ether arepreferred.

Specific examples of the oxazoline compounds include2-methoxy-2-oxazoline, 2-ethoxy-2-oxazoline, 2-propoxy-2-oxazoline,2-butoxy-2-oxazoline, 2-pentyloxy-2-oxazoline, 2-hexyloxy-2-oxazoline,2-heptyloxy-2-oxazoline, 2-octyloxy-2-oxazoline, 2-nonyloxy-2-oxazoline,2-decyloxy-2-oxazoline, 2-cyclopentyloxy-2-oxazoline,2-cyclohexyloxy-2-oxazoline, 2-allyloxy-2-oxazoline,2-methallyloxy-2-oxazoline, 2-crotyloxy-2-oxazoline,2-phenoxy-2-oxazoline, 2-cresyl-2-oxazoline,2-o-ethylphenoxy-2-oxazoline, 2-o-propylphenoxy-2-oxazoline,2-o-phenylphenoxy-2-oxazoline, 2-m-ethylphenoxy-2-oxazoline,2-m-propylphenoxy-2-oxazoline, 2-p-phenylphenoxy-2-oxazoline,2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, 2-propyl-2-oxazoline,2-butyl-2-oxazoline, 2-pentyl-2-oxazoline, 2-hexyl-2-oxazoline,2-heptyl-2-oxazoline, 2-octyl-2-oxazoline, 2-nonyl-2-oxazoline,2-decyl-2-oxazoline, 2-cyclopentyl-2-oxazoline,2-cyclohexyl-2-oxazoline, 2-allyl-2-oxazoline, 2-methallyl-2-oxazoline,2-crotyl-2-oxazoline, 2-phenyl-2-oxazoline, 2-o-ethylphenyl-2-oxazoline,2-o-propylphenyl-2-oxazoline, 2-o-phenylphenyl-2-oxazoline,2-m-ethylphenyl-2-oxazoline, 2-m-propylphenyl-2-oxazoline and2-p-phenylphenyl-2-oxazoline. Other examples of the oxazoline compoundsinclude 2,2′-bis(2-oxazoline), 2,2′-bis(4-methyl-2-oxazoline),2,2′-bis(4,4′-dimethyl-2-oxazoline), 2,2′-bis(4-ethyl-2-oxazoline),2,2′-bis(4,4′-diethyl-2-oxazoline), 2,2′-bis(4-propyl-2-oxazoline),2,2′-bis(4-butyl-2-oxazoline), 2,2′-bis(4-hexyl-2-oxazoline),2,2′-bis(4-phenyl-2-oxazoline), 2,2′-bis(4-cyclohexyl-2-oxazoline),2,2′-bis(4-benzyl-2-oxazoline), 2,2′-p-phenylenebis(2-oxazoline),2,2′-m-phenylenebis(2-oxazoline), 2,2′-o-phenylenebis(2-oxazoline),2,2′-p-phenylenebis(4-methyl-2-oxazoline),2,2′-p-phenylenebis(4,4′-dimethyl-2-oxazoline),2,2′-m-phenylenebis(4-methyl-2-oxazoline),2,2′-m-phenylenebis(4,4′-dimethyl-2-oxazoline),2,2′-ethylenebis(2-oxazoline), 2,2′-tetramethylenebis(2-oxazoline),2,2′-hexamethylenebis(2-oxazoline), 2,2′-octamethylenebis(2-oxazoline),2,2′-decamethylenebis(2-oxazoline),2,2′-ethylenebis(4-methyl-2-oxazoline),2,2′-tetramethylenebis(4,4′-dimethyl-2-oxazoline),2,2′-9,9′-diphenoxyethanebis(2-oxazoline),2,2′-cyclohexylenebis(2-oxazoline) and 2,2′-diphenylenebis(2-oxazoline).

Further other examples of the oxazoline compounds include polyoxazolinecompounds containing any of the aforesaid compounds as a monomer unit,e.g., copolymers of styrene and 2-isopropenyl-2-oxazoline. One or two ormore compounds may be arbitrarily selected from the aforesaid oxazolinecompounds for blocking the terminal carboxyl groups of the biodegradablepolyester resin (A). In terms of the heat resistance, the reactivity andthe affinity for the biodegradable polyester resin (A),2,2′-m-phenylenebis(2-oxazoline) and 2,2′-p-phenylenebis(2-oxazoline)are preferred.

Specific examples of the oxazine compounds include2-methoxy-5,6-dihydro-4H-1,3-oxazine,2-ethoxy-5,6-dihydro-4H-1,3-oxazine,2-propoxy-5,6-dihydro-4H-1,3-oxazine,2-butoxy-5,6-dihydro-4H-1,3-oxazine,2-pentyloxy-5,6-dihydro-4H-1,3-oxazine,2-hexyloxy-5,6-dihydro-4H-1,3-oxazine,2-heptyloxy-5,6-dihydro-4H-1,3-oxazine,2-octyloxy-5,6-dihydro-4H-1,3-oxazine,2-nonyloxy-5,6-dihydro-4H-1,3-oxazine,2-decyloxy-5,6-dihydro-4H-1,3-oxazine,2-cyclopentyloxy-5,6-dihydro-4H-1,3-oxazine,2-cyclohexyloxy-5,6-dihydro-4H-1,3-oxazine,2-allyloxy-5,6-dihydro-4H-1,3-oxazine,2-methallyloxy-5,6-dihydro-4H-1,3-oxazine and2-crotyloxy-5,6-dihydro-4H-1,3-oxazine. Other examples of the oxazinecompounds include 2,2′-bis(5,6-dihydro-4H-1,3-oxazine),2,2′-methylenebis(5,6-dihydro-4H-1,3-oxazine),2,2′-ethylenebis(5,6-dihydro-4H-1,3-oxazine),2,2′-propylenebis(5,6-dihydro-4H-1,3-oxazine),2,2′-butylenebis(5,6-dihydro-4H-1,3-oxazine),2,2′-hexamethylenebis(5,6-dihydro-4H-1,3-oxazine),2,2′-p-phenylenebis(5,6-dihydro-4H-1,3-oxazine),2,2′-m-phenylenebis(5,6-dihydro-4H-1,3-oxazine),2,2′-naphthylenebis(5,6-dihydro-4H-1,3-oxazine) and2,2′-P,P′-diphenylenebis(5,6-dihydro-4H-1,3-oxazine). Further otherexamples of the oxazine compounds include polyoxazine compoundscontaining any of the aforesaid compounds as a monomer unit. One or twoor more compounds may be arbitrarily selected from the aforesaid oxazinecompounds for blocking the terminal carboxyl groups of the biodegradablepolyester resin (A) such as polylactic acid.

Specific examples of the aziridine compounds include compounds obtainedby addition reaction of a mono-, bis- or poly-isocyanate compound andethyleneimine.

The terminal blocking agent (C) should be blended in the biodegradablepolyester resin (A) in an amount of 0.01 to 20 parts by mass, preferably0.05 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, basedon 100 parts by mass of the biodegradable polyester resin (A). If theblend amount is smaller than 0.01 part by mass, the hydrolysisresistance intended by the present invention cannot be provided. On theother hand, a blend amount of greater than 20 parts by mass is neithereffective nor preferable in terms of costs.

The inventive aliphatic polyester resin composition is prepared bymelt-mixing the biodegradable polyester resin (A), the crosslinkingagent (B) and the terminal blocking agent (C) by means of a commonextruder such as a uniaxial extruder or a biaxial extruder, a rollkneader, a Brabender kneader or the like. At this time, it is alsoeffective to use a static mixer or a dynamic mixer in combination withthe extruder. In order to facilitate the kneading, it is preferred touse the biaxial extruder.

In the present invention, it is preferred to add the terminal blockingagent (C) to the biodegradable polyester resin (A), knead the resultingmixture, then add the crosslinking agent (B) to the mixture and kneadthe mixture. By blending the terminal blocking agent (C) and thecrosslinking agent (B) in this order, the resin composition iseffectively imparted with the hydrolysis resistance. Therefore, it ispreferred to employ, for example, a method such that the biodegradablepolyester resin (A) and the terminal blocking agent (C) are suppliedinto a main supply port of the extruder and then the crosslinking agent(B) is added from a middle portion of the extruder or a method such thatthe biodegradable polyester resin (A) is supplied into a main supplyport of the extruder, then the terminal blocking agent (C) is added froma first feed port provided at the middle of the extruder (a feed portclosest to the main supply port) and the crosslinking agent (B) is addedfrom a second or subsequent feed port. Alternatively, the biodegradablepolyester resin (A) preliminarily terminal-blocked and the crosslinkingagent (B) may be supplied together into the extruder, and kneaded.

When the ingredients are supplied into the extruder, the ingredients maybe dry-blended, and a known transport means such as a powder feeder or apressure pump may be used.

The layered silicate (D) may be blended in the inventive aliphaticpolyester resin composition for further improvement of the moldabilityof the resin. The layered silicate may be a natural silicate or asynthetic silicate. Exemplary preparation methods for the syntheticsilicate are a melt method, an intercalation method and a hydrothermalmethod, and the silicate may be synthesized by any of these methods.Preferred examples of the layered silicate include smectites,vermiculites and swelled fluorinated mica. Examples of the smectitesinclude montmorillonite, beidellite, hectorite and saponite. Examples ofthe swelled fluorinated mica include Na-type silicon tetrafluoride mica,Na-type taeniolite and Li-type taeniolite. Among these layeredsilicates, montmorillonite and Na-type silicon tetrafluoride mica arepreferred. A cation exchange capacity is preferably 25 to 200 meq/100 g.

The layered silicate (D) is preferably blended in the biodegradablepolyester resin (A) in an amount of 0.05 to 30 parts by mass, morepreferably 0.1 to 15 parts by mass, further more preferably 0.5 to 10parts by mass, based on 100 parts by mass of the biodegradable polyesterresin (A). If the blend amount is smaller than 0.05 parts by mass,improvement of the heat resistance and the moldability cannot beexpected. On the other hand, if the blend amount is greater than 30parts by mass, it is difficult to finely disperse the layered silicatein the resin, and the resulting resin is liable to have a reducedtoughness.

It is preferred to preliminarily treat the layered silicate (D) withorganic cations. Examples of the organic cations include protonizedprimary to tertiary amines, quaternary ammoniums and organicphosphoniums. Examples of the primary amines include octylamine,dodecylamine and octadecylamine. Examples of the secondary aminesinclude dioctylamine, methyloctadecylamine and dioctadecylamine.Examples of the tertiary amines include dimethyloctylamine,dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine,dimethylpalmitylamine, dimethylstearylamine, dilaurylmonomethylamine,tributylamine, N,N-dimethylaniline, trioctylamine, dimethyldodecylamineand didodecylmonomethylamine. Examples of the quaternary ammoniumsinclude tetraethylammonium, trimethyloctadecylammonium,dimethyldioctadecylammonium, dihydroxyethylmethyloctadecylammonium,methyldodecylbis(polyethylene glycol)ammonium andmethyldiethyl(polypropylene glycol)ammonium. Examples of the organicphosphoniums include tetraethylphosphonium, tetrabutylphosphonium,tetrakis(hydroxymethyl)phosphonium and2-hydroxyethyltriphenylphosphonium. These cations may be used eitheralone or in combination.

A method for treating the layered silicate with the organic cations isto disperse the layered silicate in water or an alcohol and add a saltof the organic cations to the resulting dispersion with stirring toexchange inorganic ions of the layered silicate with the organiccations, followed by filtering, washing and drying of the resultingproduct.

Where the layered silicate (D) is used in the present invention, analkylene oxide or a compound having a hydroxycarboxylic acid unit may beadded as a dispersion improving agent to the biodegradable polyesterresin (A) for improvement of the dispersibility of the layered silicate(D) in the biodegradable polyester resin (A). Such a compound hasaffinity for both the biodegradable polyester resin and the layeredsilicate, and is easily intercalated between layers of the layeredsilicate to improve the dispersibility of the layered silicate in theresin. Examples of the alkylene oxide include polyethylene glycol andpolypropylene glycol. Examples of the compound having ahydroxycarboxylic acid unit include polylactic acid, polyhydroxybutyricacid and poly(ε-caprolactone). The compound having a hydroxycarboxylicacid unit may be a compound with its terminal carboxyl groups replacedwith hydroxyl groups (e.g., polycaprolactondiol). The compound to beused as the dispersion improving agent preferably has a number averagemolecular weight of 200 to 50,000, more preferably 500 to 20,000. If themolecular weight is smaller than 200, a gas will emanate during themolding or bleed-out from the resulting molded article will occur. Ifthe molecular weight is higher than 50,000, the intercalation of thecompound between the layers of the layered silicate will beinsufficient.

The dispersion improving agent is preferably blended in thebiodegradable polyester resin (A) in an amount of 0.01 to 20 parts bymass, more preferably 0.02 to 10 parts by mass, based on 100 parts bymass of the biodegradable polyester resin (A). If the blend amount issmaller than 0.01 part by mass, the effect of the addition of thedispersion improving agent will be small. If the blend amount is greaterthan 20 parts by mass, the mechanical strength and the heat resistanceof the resin will be reduced. Exemplary methods for blending thedispersion improving agent include a method such that the layeredsilicate (D) is preliminarily impregnated with the dispersion improvingagent, a method such that the dispersion improving agent is mixed withthe layered silicate (D) in the presence of water or an organic solventand then the water or the organic solvent is removed by filtering or thelike, a method such that the dispersion improving agent is added whenthe biodegradable polyester resin and the layered silicate aremelt-kneaded, and a method such that the dispersion improving agent isadded together with the layered silicate when the biodegradablepolyester resin is synthesized. Among these methods, the method ofpreliminarily mixing the dispersion improving agent with the layeredsilicate is preferred.

A pigment, a heat stabilizer, an antioxidant, a weather resistant agent,a flame retarder, a plasticizer, a lubricant, a mold release agent, anantistatic agent, a filler or the like may be added to the inventivealiphatic polyester resin composition, as long as the properties of thealiphatic polyester resin composition are not significantlydeteriorated. Examples of the heat stabilizer and the antioxidantinclude hindered phenols, phosphorus compounds, hindered amines, sulfurcompounds, copper compounds and halides of alkali metals, and mixturesof any of these compounds. The heat stabilizer, the antioxidant, theweather resistant agent or a like additive is generally added during themelt kneading or the polymerization. Exemplary inorganic fillers includetalc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina,magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate,sodium aluminosilicate, magnesium silicate, glass balloon, carbon black,zinc oxide, antimony trioxide, zeolites, hydrotalcite, metal fibers,metal whiskers, ceramic whiskers, potassium titanate, boron nitride,graphite, glass fibers and carbon fibers. Exemplary organic fillersinclude naturally existing polymers such as starch, cellulose particles,wood powder, bean curd refuse, chaff, wheat bran and kenaf, and productsobtained by modifying these polymers.

A method for mixing another thermoplastic resin and/or the filler withthe inventive aliphatic polyester resin composition is not particularlylimited. For example, the aliphatic polyester resin, the thermoplasticresin and/or the filler are kneaded by means of a uniaxial extruder, abiaxial extruder, a roll kneader, a Brabender kneader or the like afterheating and melting. It is also effective to use a static mixer or adynamic mixer in combination with the aforesaid extruder.

Various articles can be molded from the inventive aliphatic polyesterresin composition by a known molding method. At least one molding methodselected from an injection molding method, a blow molding method, anextrusion molding method and a foam molding method is preferably used.

An ordinary injection molding method as well as a gas injection moldingmethod, an injection press molding method and an expansion injectionmolding method may be employed as the injection molding method. Acylinder temperature for the injection molding should be not lower thanthe melting point Tm or the fluidizing temperature of the resin,preferably 180 to 230° C., more preferably 190 to 220° C. If the moldingtemperature is too low, short molding will occur to result in unstablemolding, and overload is liable to occur. On the other hand, if themolding temperature is too high, the aliphatic polyester resin will bedecomposed and, therefore, the resulting molded article will have areduced strength or be colored. The temperature of a mold should be nothigher than Tm−20° C. Where the crystallization of the biodegradablepolyester resin in the mold is to be promoted for increasing the heatresistance of the biodegradable polyester resin, the mold temperature ispreferably kept at a temperature of Tg+20° C. to Tm−20° C. for apredetermined period and then cooled to not higher than Tg. Where thecrystallization of the resin in the mold is not required, the moldtemperature may be immediately cooled to not higher than Tg. Wherepost-crystallization is required, heat treatment is preferably performedat a temperature of Tg to Tm−20° C.

Exemplary blow molding methods to be employed for producing ablow-molded article from the inventive aliphatic polyester resincomposition include a direct blow molding method in which the article ismolded directly from material chips, an injection blow molding method inwhich a preform (bottomed parison) prepared by injection molding isblow-molded, and a draw blow molding method. Further, a hot parisonmethod in which a preform is blow-molded immediately after preparationof the preform, or a cold parison method in which a preform is oncecooled and taken out and then reheated to be blow-molded may beemployed. A temperature for the blow molding should be Tg+20° C. toTm−20° C. If the blow molding temperature is lower than Tg+20° C., themolding will be difficult, and the resulting blow-molded container willhave an insufficient heat resistance. On the other hand, if the blowmolding temperature is higher than Tm−20° C., the resulting blow-moldedcontainer is liable to have an uneven wall thickness, and draw-down willoccur due to reduction of viscosity.

The extrusion molding method to be employed for producing anextrusion-molded article from the inventive aliphatic polyester resincomposition will be described. A T-die method or a round die method maybe employed as the extrusion molding method. A temperature for theextrusion molding should be not lower than the melting point Tm or thefluidizing temperature of the aliphatic polyester resin composition,preferably 180 to 230° C., more preferably 190 to 220° C. If the moldingtemperature is too low, unstable molding will result, and overload isliable to occur. On the other hand, if the molding temperature is toohigh, the biodegradable polyester resin (A) will be decomposed and,therefore, the resulting extrusion-molded article will have a reducedstrength or be colored. Sheets, pipes and the like are produced by theextrusion molding. For improvement of the heat resistance of thesearticles, a heat treatment may be performed at a temperature not lowerthan the glass transition temperature (Tg) of the aliphatic polyesterresin composition and not higher than Tm−20° C.

The sheets thus produced may be deep-drawn, for example, by vacuumforming, air pressure forming or vacuum air pressure forming.Temperatures for the deep drawing and the heat treatment are preferablyfrom Tg+20° C. to Tm−20° C. If the deep drawing temperature is lowerthan Tg+20° C., the deep drawing will be difficult, and the resultingcontainer is liable to have an insufficient heat resistance. On theother hand, if the deep drawing temperature is higher than Tm−20° C.,the resulting container is liable to have an uneven wall thickness and apoorer impact resistance with its orientation lost.

Any common foaming methods may be employed for producing a foamedarticle from the inventive aliphatic polyester resin composition. Bymeans of an extruder, for example, a foaming agent decomposable at themelting point of the resin is preliminarily blended with the resin andthe resulting mixture is extruded from a slit-like nozzle into a sheetor from a round nozzle into a strand. Examples of the decomposablefoaming agent include azo compounds such as azodicarbonamides and bariumazodicarboxylates, nitroso compounds such asN,N′-dinitrosopentamethylenetetramine, hydrazine compounds such as4,4′-oxybis(benzene sulfonyl hydrazide) and hydrazicarbonamide, andinorganic foaming agents such as sodium hydrogencarbonate.Alternatively, a volatile foaming agent may be injected from a middleportion of the extruder for foaming the resin. Examples of such afoaming agent include inorganic substances such as nitrogen, carbondioxide and water, and organic solvents typified by hydrocarbons such asmethane, ethane, butane and pentane, fluorinated compounds and alcoholssuch as ethanol and methanol. Further, foamed particles may be producedby preparing particles of the resin composition, preliminarilyimpregnating the resin particles with the organic solvent, water or alike foaming agent, and changing the temperature and/or the pressure tofoam the resin particles.

By employing any of the aforesaid molding methods, various moldedarticles can be produced from the inventive aliphatic polyester resincomposition. Specific examples of the molded articles include tablewaresuch as dishes, bowls, pots, chopsticks, spoons, forks and knives,containers for fluids, container caps, rulers, stationery such aswriting utensils, clear cases and CD cases, daily commodities such assink corner strainers, trash boxes, washbowls, tooth brushes, combs andhangers, agricultural and horticultural materials such as flower potsand seeding pots, toys such as plastic models, electrical applianceresin components such as air conditioner panels, refrigerator trays andhousings, and automotive resin components such as bumpers, interiorpanels and door trims.

Specific examples of the containers for fluids include drinking cups andbeverage bottles for milk beverages, cold beverages and alcoholicbeverages, temporary storage containers for seasonings such as soysauce, sauce, mayonnaise, ketchup and cooking oil, containers forshampoo and rinse, cosmetic containers, and agricultural containers. Theshapes of the containers for fluids are not particularly limited, butthe containers preferably have a depth of not smaller than 5 mm forcontaining the fluids. The wall thicknesses of the containers are notparticularly limited, but are preferably not smaller than 0.1 mm, morepreferably 0.1 to 5 mm, for strength.

Sheets and pipes can be produced from the inventive aliphatic polyesterresin composition. Specific applications of the sheets and the pipesinclude material sheets for deep drawing, material sheets for batchfoaming, cards such as credit cards, desk pads, clear files, straws, andagricultural and horticultural rigid pipes. Further, the sheets may bedeep-drawn for production of deep-drawn articles such as foodcontainers, agricultural and horticultural containers, blister packagesand press-through packages. The shapes of the deep-drawn articles arenot particularly limited, but the deep-drawn articles preferably havedepths of not smaller than 2 mm for containing food, goods and drugs.Further, the deep-drawn articles preferably have wall thicknesses of notsmaller than 50 μm, more preferably 150 to 500 μm. Specific examples ofthe food containers include fresh food trays, instant food containers,fast food containers and lunch boxes. Specific examples of theagricultural and horticultural containers include seeding pots. Specificexamples of the blister packages include food containers as well aspackages for various commodities including stationery, toys and drybatteries.

Examples of the foamed articles produced from the inventive resincomposition include: bulk containers, pads for iron containers andcushioning materials in a packaging field; binders, cut files and cutboxes in a stationery field; core materials for partitions, sign boards,buffer wall materials and camping floor boards in an architecturalfield; cases for video cameras and cassettes and core materials for OAcases in an electrical appliance field; fresh food packages,confectionery packages and food trays in a food field; door mats, toiletmats, kitchen mats, bath mats, garden mats, mats for hospitals, screenmaterials and animal rejection fences in a daily commodity materialfield; seed beds and cases for hydroponic seed bases in an agriculturalmaterial field; and fish net buoys, fishing floats, oil fence buoys andcooler boxes in a fishery material field.

According to the present invention, the aliphatic polyester resincomposition excellent in heat resistance, moldability and hydrolysisresistance can be provided by an industrially feasible technique. Theresin composition can be used for injection molding and blow molding.Articles molded from the resin composition maintain their physicalproperties even during use under severely humid and hot conditions andduring prolonged storage.

EXAMPLES

The present invention will hereinafter be described further specificallyby way of examples. However, it should be understood that the inventionbe not limited to the following examples.

The following measurement methods were employed for evaluation ofExamples and Comparative Examples described blow.

(1) Molecular Weight

The weight average molecular weight of polylactic acid was determined at40° C. with the use of tetrahydrofuran as an eluent by means of a gelpermeation chromatography (GPC) device (available from Shimadzu Co.,Ltd.) having a differential refractometer, and expressed on the basis ofpolystyrene calibration standards. A sample was dissolved in chloroformand diluted by THF.

(2) Flexural Breakdown Strength

In conformity with ASTM-790, a test strip having asizeof 150 mm×10mm×3.2 mm was prepared, and the flexural breakdown strength was measuredwith a load being applied to the test strip at a deformation rate of 1mm/min.

(3) Melt Flow Rate (MFR)

In conformity with JIS K7210, the melt flow rate was measured underconditions D specified in Table 1 of Appendix A of JIS K7210 (with aload of 21.2N at a test temperature of 190° C.).

(4) Crystallization Rate Index (See FIG. 1)

With the use of a DSC machine (Pyrisl DSC available form Perkin ElmerCorporation), a sample was heated at a temperature increasing rate of+500° C./min from 20° C. to 200° C., and kept at 200° C. for 5 minutes.Then, the sample was cooled at a temperature decreasing rate of −500°C./min from 200° C. to 130° C., and kept at 130° C. for crystallization.With the final crystallinity (O) defined as 1, as shown in a graph ofFIG. 1, time required for the crystallinity to reach 0.5 was determinedas the crystallization rate index (min).

(5) Amount of Terminal Carboxyl Groups

First, 0.15 g of a resin was dissolved in 20 ml of methylene chloride,and an indicator (Phenol Red) was added to the resulting solution. Then,the solution was titrated with a 0.1N KOH solution.

(6) Evaluation of Injection Moldability

With the use of an injection molding machine (IS-100E available fromToshiba Machine Co., Ltd.), a resin was injection-molded in a releasablecup mold (having a diameter of 38 mm and a height of 300 mm and kept ata temperature of 110° C.) at a molding temperature of 200° C., and aminimum cycle time required for proper release of a cup was determined.

(7) Evaluation of Hydrolysis Resistance

A test strip having a size of 150 mm×10 mm×3.2 mm in conformity withASTM-790 and pellets were stored in a constant temperature/constanthumidity chamber (Model IW221 available from Yamato Science Co., Ltd.)at a temperature of 60° C. and a humidity of 95% for 15 to 30 days.Then, the flexural breakdown strength of the test strip was measured,and the MFR of the pellets was measured after the pellets were dried at50° C. for 50 hours in a vacuum condition. The flexural breakdownstrength was evaluated as a retention ratio (%) which was determined onthe basis of an initial flexural breakdown strength.

Ingredients and auxiliary materials used for Examples and ComparativeExamples are as follows.

A. Biodegradable Polyester Resins

-   -   Resin A: Polylactic acid (having a weight average molecular        weight of 200,000, an L-lactic acid ratio of 99%, a D-lactic        acid ratio of 1%, a melting point of 168° C. and an MFR of 3        g/10 min)    -   Resin B: A blend containing the resin A (polylactic acid) and a        copolymer of terephthalic acid, adipic acid and 1,4-butandiol        (having a melting point of 108° C. and an MFR of 5 g/10 min) in        a mass ratio of 90/10        B. Crosslinking Agents        (1) (Meth)Acrylate Compounds    -   PEGDM: Polyethylene glycol dimethacrylate (available from Nippon        Yushi Co., Ltd., and having an ethylene glycol polymerization        degree of 4)    -   EGDM: Ethylene glycol dimethacrylate (available from Nippon        Yushi Co., Ltd.)    -   DEGDM: Diethylene glycol dimethacrylate (available from Nippon        Yushi Co., Ltd.)        (2) Polyvalent Isocyanate Compound    -   HMDI: Hexamethylene diisocyanate (available from Nakarai        chemical Ltd.)    -   Di-t-butylperoxide (available from Nippon Yushi Co., Ltd.) was        used as a crosslinking assist agent.        C. Terminal Blocking Agents    -   CDI: N,N′-di-2,6-diisopropylphenylcarbodiimide (STABAKSOL I        available from Bayer Corporation)    -   CDP: Aromatic polycarbodiimide (STABAKSOL P available from Bayer        Corporation)    -   CDC: Polycyclohexylcarbodiimide (LA-1 available from Nisshinbo        Industries, Inc.)    -   EPX: p-t-butylphenyl glycidyl ether (DENACOL EX-146 available        from Nagase Chemical Co., Ltd.)    -   EX: Ethylene glycol diglycidyl ether (DENACOL EX-810 available        from Nagase Chemical Co., Ltd.)    -   OXZ: 2,2′-m-phenylenebis(2-oxazoline) (available from Tokyo        Chemical Industry Co., Ltd.)        D. Layered Silicate    -   SBN-E: Montmorillonite with its interlayer ions replaced by        trimethyloctadecylammonium ions (available from Hojun Co., Ltd.        and having an average particle diameter of 2.5 μm)    -   MEE: Synthesized fluorinated mica with its interlayer ions        replaced by dihydroxyethylmethyldodecylammonium ions (available        from Corp Chemical Co., Ltd. and having an average particle        diameter of 6.3 μm)

Example 1

First, 100 parts by mass of the resin A and 0.8 parts by mass of theterminal blocking agent CDI were dry-blended and supplied into a hopperof a biaxial extruder (PCM-30 available from Ikegai Co., Ltd., andhaving a die having three 4-mm diameter holes, an extrusion headtemperature of 210° C. and a die outlet temperature of 190° C.). Then, asolution containing 0.2 parts by mass of PEGDM and 0.4 parts by mass ofthe crosslinking assist agent dissolved in 1 part by mass of anacetyltributyl citrate plasticizer was injected into a middle portion ofa kneader by means of a pump. The resulting mixture was extruded,pelletized and dried. Thus, an aliphatic polyester resin composition wasprepared. The results of the evaluation of the physical properties andthe hydrolysis resistance of the composition thus prepared are shown inTable 1.

Examples 2 to 18 and Comparative Examples 1 to 6

Resin compositions were prepared in substantially the same manner as inExample 1, except that different types and amounts of biodegradablepolyester resins, crosslinking agents, lamellar silicates and terminalblocking agents were used as shown in Table 1. Then, the resincompositions were evaluated. The results of the evaluation are shown inTable 1. In Examples 5, 6, 8, 9, 11, 12 and 13 and Comparative Example4, the addition of the layered silicate was achieved by dry-blending thebiodegradable polyester resin and the layered silicate and supplying theresulting mixture into the hopper.

Example 19

First, 100 parts by mass of the resin A was supplied into the hopper ofthe same biaxial extruder as employed in Examples 1 to 18. Then, asolution containing 0.2 parts by mass of PEGDM and 0.4 parts by mass ofthe crosslinking assist agent dissolved in 1 part by mass of anacetyltributyl citrate plasticizer was injected into a first feed portprovided at the middle of the kneader (a feed port closest to thehopper) by means of a pump, and 1.5 parts by mass of the terminalblocking agent CDI was supplied into a second feed port by a feeder. Theresulting mixture was extruded, pelletized and dried. Thus, an aliphaticpolyester resin composition was prepared. The results of the evaluationof the resin composition are shown in Table 1. TABLE 1 Example 1 2 3 4 56 7 8 Major ingredients for resin composition (parts by mass)Biodegradable resin Type A A A A A A A A Amount 100 100 100 100 100 100100 100 Crosslinking agent Type PEGDM PEGDM PEGDM PEGDM PEGDM PEGDM HMDIHMDI Amount 0.2 0.2 0.2 0.2 0.2 0.2 0.05 0.05 Layered silicate Type — —— — SBN-E MEE — SBN-E Amount 0 0 0 0 4 4 0 4 Terminal blocking agentType CDI CDI CDI CDI CDI CDI CDI CDI Amount 0.5 1.5 2.0 8.0 2.0 2.0 2.02.0 Physical properties of Composition Flexural breakdown strength (MPa)130.1 129.6 129.3 127.8 112.0 109.2 130.4 119.2 MFR (g/10 min) 1.1 1.11.2 1.3 0.8 0.9 1.5 1.3 Crystallization rate index (min) 1.4 1.4 1.4 1.51.0 1.1 1.6 1.1 Amount of terminal carboxyl groups (mol/t) 4 1 0 0 0 1 01 Moldability Injection molding cycle (sec) 58 58 58 59 39 41 62 42Evaluation of hydrolysis resistance* 15 Flexural breakdown (MPa) 122.3127.0 129.2 127.9 107.5 103.7 129.1 112.0 days strength Retention ratio(%) 94 98 100 100 96 95 99 94 MFR (g/10 min) 1.6 1.4 1.3 1.3 1.1 1.3 1.81.7 30 Flexural breakdown (MPa) 117.1 121.8 125.4 126.5 100.8 98.3 121.3101.3 days strength Retention ratio (%) 90 94 97 99 90 90 93 85 MFR(g/10 min) 2.2 1.8 1.5 1.5 1.8 2.0 2.5 2.7 Example 9 10 11 12 13 14 1516 Major ingredients for resin composition (parts by mass) Biodegradableresin Type A B B A A A A A Amount 100 100 100 100 100 100 100 100Crosslinking agent Type HMDI PEGDM PEGDM PEGDM PEGDM PEGDM PEGDM PEGDMAmount 0.05 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Layered silicate Type MEE —SBN-E SBN-E SBN-E — — — Amount 4 0 4 4 4 0 0 0 Terminal blocking agentType CDI CDI CDI EPX OXZ CDP CDC EX Amount 2.0 2.0 2.0 2.0 2.0 0.5 0.52.0 Physical properties of Composition Flexural breakdown strength (MPa)114.4 113.0 113.0 110.3 113.0 129.8 128.9 108.2 MFR (g/10 min) 1.4 1.41.1 0.9 0.8 1.1 1.1 1.0 Crystallization rate index (min) 1.3 3.5 3.1 1.01.1 1.4 1.4 1.1 Amount of terminal carboxyl groups (mol/t) 0 1 1 3 5 1 31 Moldability Injection molding cycle (sec) 44 60 39 40 40 58 58 42Evaluation of hydrolysis resistance* 15 Flexural breakdown (MPa) 106.4110.7 106.2 99.3 96.1 126.4 125.1 105.1 days strength Retention ratio(%) 93 98 94 90 85 97 97 97 MFR (g/10 min) 1.9 1.6 1.5 1.8 2.1 1.4 1.41.2 30 Flexural breakdown (MPa) 95.0 100.6 92.7 83.8 78.0 120.6 119.4101.8 days strength Retention ratio (%) 83 89 82 76 69 93 93 94 MFR(g/10 min) 3.1 2.3 2.4 3.9 4.8 1.7 1.8 1.4 Example Comparative Example17 18 19 1 2 3 4 5 6 Major ingredients for resin composition (parts bymass) Biodegradable resin Type A A A A A A A B B Amount 100 100 100 100100 100 100 100 100 Crosslinking agent Type DEGDM EGDM PEGDM — PEGDMPEGDM HMDI PEGDM PEGDM Amount 0.2 0.2 0.2 0.0 0.2 0.2 0.05 0.2 0.2Layered silicate Type — — — — — SBN-E — — SBN-E Amount 0 0 0 0 0 4 0 0 4Terminal blocking agent Type CDI CDI CDI CDI — — — — — Amount 2.0 2.03.0 1.5 0 0 0 0 0 Physical properties of Composition Flexural breakdownstrength (MPa) 128.5 128.1 129.9 110.9 136.2 111.2 138.5 138.0 112.0 MFR(g/10 min) 1.2 1.2 1.1 3.1 1.1 0.8 1.4 1.4 1.1 Crystallization rateindex (min) 1.4 1.4 1.4 105 1.4 1.0 1.6 3.5 3.1 Amount of terminalcarboxyl groups (mol/t) 0 0 2 0 22 26 23 25 27 Moldability Injectionmolding cycle (sec) 58 58 58 ≧600 58 39 61 60 40 Evaluation ofhydrolysis resistance* 15 Flexural breakdown (MPa) 128.4 128.0 117.299.8 12.9 0.5 8.3 5.5 1.3 days strength Retention ratio (%) 100 100 9090 9 0.4 6 4 1 MFR (g/10 min) 1.2 1.2 1.7 4.5 — — — — — 30 Flexuralbreakdown (MPa) 127.1 126.0 102.4 61.0 — — — — — days strength Retentionratio (%) 99 98 79 55 — — — — — MFR (g/10 min) 1.3 1.4 3.4 18.2 — — — ——*Symbol - in evaluation means that measurement was impossible. (Forflexural breakdown strength, test strips had strength insufficient forthe measurement. For MFR, samples had an extremely reduced molecularweight such that polymer's nature was lost.)*Crosslinking agent and terminal blocking agent were added in this orderin Example 19, and in reverse order in other examples.

As apparent from Table 1, the resin compositions of Examples 1 to 19were excellent in injection moldability with higher crystallization rateindices. These resin compositions maintained their physical properties(e.g., strength) even after having been stored under the severely humidand hot conditions for the evaluation of the hydrolysis resistance.

On the contrary, the resin composition of Comparative Example 1 had alower crystallization rate, a longer injection molding cycle and apoorer moldability, because no crosslinking agent was added. Further,the hydrolysis resistance was poorer.

The resin compositions of Comparative Examples 2 to 6 had virtually nohydrolysis resistance, because no terminal blocking agent was added.

Further, the following facts are revealed.

A comparison between Example 2 and Comparative Example 1 shows that theresin composition of Example 2 with the polylactic acid crosslinked bythe PEGDM had a significantly higher crystallization rate and asignificantly shorter injection molding cycle than the resin compositionof Comparative Example 1. Although the same type and amount of terminalblocking agent was used, the resin composition of Example 2 was moreexcellent in hydrolysis resistance. Therefore, the resin compositionprepared by utilizing the terminal blocking and the crosslinking incombination was more excellent in physical property retention under thehigh temperature and high humidity conditions than the terminal-blockedresin.

A comparison between Examples 1 to 4 and Comparative Example 2 showsthat the resin compositions of Examples 1 to 4 maintained their physicalproperties even after having been stored under the high temperature andhigh humidity conditions for the evaluation of the hydrolysisresistance, because proper amounts of the terminal blocking agent wereused for the terminal blocking. In Examples 1 to 4, different amounts ofthe terminal blocking agent ranging from 0.5 to 8 parts by mass wereadded and, as a result, it was found that the physical propertyretention ratio was increased correspondingly to the amounts of theadded terminal blocking agent.

In Examples 5 and 6, the addition of the layered silicate increased thecrystallization rate thereby to reduce the injection molding cycle ascompared with Example 3 in which the resin composition was preparedsubstantially in the same manner except that no layered silicate wasadded. Although Example 5 and Comparative Example 3 differ in whether ornot the terminal blocking agent was added, the resin composition ofExample 5 with the terminal-blocked resin maintained its physicalproperties even after having been stored under the high temperature andhigh humidity conditions for the evaluation of the hydrolysisresistance.

Examples 7 to 9 in which the polylactic acid was crosslinked by theisocyanate compound (HMDI) provided the same effect as Examples 3, 5 and6 in which the polylactic acid was crosslinked by the PEGDM.

In Examples 10 and 11, the blend of the polylactic acid and thecopolymer of terephthalic acid, adipic acid and 1,4-butandiol was usedas the biodegradable resin, but the addition of the crosslinking agentor the addition of the crosslinking agent and the layered silicateincreased the crystallization rate and reduced the injection moldingcycle. Although Examples 10 and 11 differ from Comparative Examples 5and 6 in whether or not the terminal blocking agent was added, the resincomposition with the terminal-blocked resin maintained its physicalproperties even after having been stored under the high temperature andhigh humidity conditions for the evaluation of the hydrolysisresistance.

In Examples 12 and 13 in which the resin was terminal-blocked by theepoxy compound and the oxazoline compound, respectively, the physicalproperties were maintained even after storage under the high temperatureand high humidity conditions for the evaluation of the hydrolysisresistance.

In Examples 14 and 15 in which CDP and CDC were respectively employed asthe terminal blocking agent unlike in Example 1, the crystallizationrate indices and the injection molding cycles were equivalent to thoseof Example 1, and the hydrolysis resistance was slightly improved ascompared with Example 1.

In Example 16 in which EX was employed as the terminal blocking agentunlike in Example 1, the crystallization rate index, the injectionmolding cycle and the hydrolysis resistance were slightly improved ascompared with Example 1.

In Examples 17 and 18, the (meth)acrylate compound having shorterethylene glycol chains was employed instead of PEGDM for thecrosslinking, but physical properties equivalent to those of Example 3were provided.

In Example 19, the crosslinking agent and the terminal blocking agentwere added in reverse order as compared with Examples 1 to 18. As aresult, the crystallization rate and the injection molding cycle wereequivalent to those in Examples 1 to 3, but the hydrolysis resistancewas slightly poorer even with the addition of a greater amount of theterminal blocking agent as compared with Examples 1 to 3. However, thehydrolysis resistance was significantly improved as compared withComparative Example 1 in which the crosslinking agent was not added.Therefore, the resin composition of Example 19 had sufficientlypractical properties.

1. An aliphatic polyester resin composition comprising a biodegradablepolyester resin (A) which essentially comprises an α- and/orβ-hydroxycarboxylic acid unit and is crosslinked by at least onecrosslinking agent (B) selected from the group consisting of(meth)acrylate compounds and polyvalent isocyanate compounds, whereinsome or all of carboxyl groups of the resin (A) are blocked by 0.01 to20 parts by mass of a terminal blocking agent (C) based on 100 parts bymass of the resin (A).
 2. An aliphatic polyester resin composition asset forth in claim 1, wherein the terminal blocking agent (C) is atleast one compound selected from the group consisting of carbodiimidecompounds, epoxy compounds, oxazoline compounds, oxazine compounds andaziridine compounds.
 3. An aliphatic polyester resin composition as setforth in claim 1, wherein the crosslinking agent (B) is present in aproportion of 0.01 to 10 parts by mass based on 100 parts by mass of thebiodegradable polyester resin (A).
 4. An aliphatic polyester resincomposition as set forth in claim 1, wherein the biodegradable polyesterresin (A) essentially comprises one of poly(L-lactic acid),poly(D-lactic acid), a copolymer of L-lactic acid and D-lactic acid anda blend of poly(L-lactic acid) and poly(D-lactic acid).
 5. An aliphaticpolyester resin composition as set forth in claim 1, further comprising0.05 to 30 parts by mass of a layered silicate (D) based on 100 parts bymass of the biodegradable polyester resin (A).
 6. A method for preparingan aliphatic polyester resin composition which comprises a biodegradablepolyester resin (A) essentially comprising an α- and/orβ-hydroxycarboxylic acid unit and crosslinked by at least onecrosslinking agent (B) selected from the group consisting of(meth)acrylate compounds and polyvalent isocyanate compounds, whereinsome or all of carboxyl groups of the resin (A) are blocked by 0.01 to20 parts by mass of a terminal blocking agent (C) based on 100 parts bymass of the resin (A), the method comprising: mixing the biodegradablepolyester resin (A) and the terminal blocking agent (C); and then mixingthe crosslinking agent (B) with the resulting mixture.
 7. A moldedarticle or a foamed article produced from an aliphatic polyester resincomposition as recited in claim
 1. 8. A molded article or a foamedarticle produced from an aliphatic polyester resin composition asrecited in claim
 2. 9. A molded article or a foamed article producedfrom an aliphatic polyester resin composition as recited in claim
 3. 10.A molded article or a foamed article produced from an aliphaticpolyester resin composition as recited in claim
 4. 11. A molded articleor a foamed article produced from an aliphatic polyester resincomposition as recited in claim 5.